App.xaml.cs

        public App()
        {
            this.InitializeComponent();
            this.Suspending += OnSuspending;
            SignalR();
        }
        public void SignalR()
        {
            conn = new HubConnection("http://<your-mobile-app>.azurewebsites.net");
            proxy = conn.CreateHubProxy("ChatHub");
            conn.Start();
            
            proxy.On<ChatMessage>("broadcastMessage", OnMessage);
            
        }
        public void Broadcast(ChatMessage msg)
        {
            proxy.Invoke("Send", msg);
        }
        private async void OnMessage(ChatMessage msg)
        {
            await Windows.ApplicationModel.Core.CoreApplication.MainView.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
            {
                ChatVM.Messages.Add(msg);
            });           
        }